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Alkenes and Alkynes

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aka unsaturated compounds organic compounds that contain ... 1. React quickly with small, diatomic molecules (ie hydrogen, halogens) 2. Participates in: ... – PowerPoint PPT presentation

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Title: Alkenes and Alkynes


1
Lesson 3
  • Alkenes and Alkynes

2
Alkenes (CnH2n)
  • Organic compounds that contain double
    carbon-carbon bonds
  • aka unsaturated compounds organic compounds
    that contain double and triple bonds
  • General formula CnH2n

3
Alkynes (CnH2n-2)
  • Organic compounds that contain triple
    carbon-carbon bonds
  • General formula CnH2n-2

4
Naming Alkenes and Alkynes
  • Step 1 Find the longest continuous chain that
    contains the double or triple bond(s) (parent
    chain).

5
  • Step 2 Number the chain, starting at the end of
    the chain closest to the double or triple bond.
    Use appropriate prefix to indicate the number of
    carbon atoms in the parent chain of the alkene.

6
  • Step 3 Use the ending -ene to indicate that it
    is an alkene (double bond) or -yne for an
    alkyne (triple bond).

7
  • Step 4 Branches on alkenes or alkynes are named
    and numbered in the same way as branched alkanes.

8
Drawing Alkenes and Alkynes
  • Step 1 Draw a straight chain containing the
    number of carbon atoms indicated by the name of
    the parent carbon chain.

9
  • Step 2 Number the carbon atoms in the parent
    chain from left to right.

10
  • Step 3 Double or triple bonds are inserted in the
    parent chain after the carbon as numbered in the
    name.

11
  • Step 4 Attach all branches to their numbered
    locations

12
  • Step 5 Add enough hydrogens so that all carbons
    will have four bonds.

13
Alkene Properties
  • 1. React quickly with small, diatomic molecules
    (ie hydrogen, halogens)

14
  • 2. Participates in
  • addition reactions converts unsaturated
    hydrocarbons to saturated hydrocarbons
  • hydrogenation addition reactions which convert
    unsaturated hydrocarbons to saturated ones by the
    addition of hydrogen only.

15
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16
  • Used as starting materials in the petrochemical
    industry for the manufacture of gasoline,
    plastics, etc.
  • 4. No rotation around a carbon-carbon double bond
  • 5. Alkenes are non-polar

17
  • Alkenes are unsaturated (contain all single C-C
    bonds and have the maximum number of hydrogens)
  • Structural isomers exist for all alkenes larger
    than propene

18
  • LDFs only
  • As the number of carbons increase, boiling and
    melting points increase also

19
Alkyne Properties
  • No rotation around carbon-carbon multiple bonds.
  • React in addition and hydrogenation
  • reactions.
  • 3. As the number of carbons increase, boiling and
    melting points increase also.

20
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21
  • Alkynes are non-polar and are soluble in
    non-polar solvents only.
  • LDFs only
  • Alkynes are unsaturated
  • Structural isomers exist for alkynes larger than
    propyne

22
Geometric Isomerism
  • Isomers of alkenes that differ only in the
    arrangement of their substituted groups
  • Possible whenever each carbon of the double bond
    has at least one substituent
  • Isomers will differ with respect to their
    physical and chemical properties

23
  • Trans substituted groups are on opposite sides
    of the double bond
  • Cis substituted groups are on the same side of
    the double bond
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